A wide variety of seat belt retractors for vehicles have been developed to prevent protraction of the seat belt. Many such retractors respond to prevent seat belt protraction during periods evidencing emergency conditions. These seat belt retractors commonly comprise a reel, upon which a seat belt is wound, having a ratchet wheel with teeth to be engaged by a pivotally frame-mounted pawl. The pawl is normally biased in a non-engaging position in which the pawl is spaced from the ratchet wheel, and to prevent belt protraction, an emergency activation device actuates the pawl into engagement with the ratchet wheel. This is to prevent protraction of the seat belt during instances evidencing emergency conditions. A common emergency activation device is an inertial mechanism which operates in response to vehicle accelerations or decelerations greater than a predetermined value.
More particularly, during vehicle operation periods of constant speed or modest acceleration or deceleration, the pawl is typically biased, such as by gravity, to its non-engaging position with respect to the ratchet wheel. The inertial mechanism responds to changes in acceleration or deceleration greater than a predetermined value to urge the pawl into engagement with the ratchet teeth. That is, in an emergency locking retractor employing an inertial device, the seat belt is unrestrained against protraction under normal vehicle operation, and when the inertial device responds to vehicle acceleration or deceleration greater than a predetermined value, the inertial mechanism forces the pawl to pivot into engagement with the teeth of the ratchet wheel to prevent belt protraction.
To exceed the predetermined value in some inertial mechanisms, some minimum change in acceleration or deceleration, even though slight in some instances, is required in order for the inertial mechanism to actuate the pawl into engagement with the ratchet wheel. However, there may be times when an emergency condition exists and goes unnoticed by the inertial mechanism because the change in acceleration or deceleration is not greater than the predetermined value. For example, when a vehicle slides across a surface having a low coefficient of friction, such as a surface covered with ice, standing water or gravel, the vehicle may not accelerate or decelerate by a value greater than the predetermined value necessary to be noticed by the inertial mechanism. As a result, the inertial mechanism may not actuate the pawl into engagement with ratchet wheel to prevent protraction of the seat belt.
In this connection, effort has been directed to activation mechanisms which respond to other features of a vehicle, such as braking systems used in vehicles. With activation mechanisms that respond to braking systems, advantages include having a retractor which is not entirely dependant upon an inertial mechanism and which, in some instances, would lock up earlier because the braking systems would be activated before the inertial mechanism could experience the required change in acceleration or deceleration. Furthermore, vehicle operators, in many instances, tend to apply the vehicle's brakes upon surfaces which have a low coefficient of friction.
An example of a brake activated safety device is disclosed in U.S. Pat. No. 3,220,747. In this example, a seat belt retractor is automatically operable in response to excessive emergency application of the vehicle's brake system. A disadvantage with this type of activation includes the inability to be adapted to today's common retractors which use ratchet mechanisms having a pawl to lock the retractor against belt protraction. Another disadvantage tends to be that some vehicle operators may not be able to apply sufficient force to the brake pedal or that some vehicle operators may lightly pump the brake pedal to prevent the tires from locking up, such as on surfaces having a low coefficients of friction. As a result, the activation mechanism may not effectively actuate to lock the retractor against belt protraction due to a lack of excessive braking force to the foot pedal.
Another example of a brake activated seat belt retractor is disclosed in U.S. Pat. No. 3,797,603 . In this example, a seat belt retractor is actuated upon application of a brake system and/or an inertial system. More particularly, a magnet supplied with current maintains the retractor so the belt is free to be protracted, and upon interruption of the current, the retractor locks up to prevent protraction of the belt. Such current interruption is upon opening of a pressure switch responsive to the hydraulic pressure in a vehicle's brake system and/or the opening of an inertial switch responsive to a change in acceleration of the vehicle.
However, a disadvantage with this type of brake pedal activation mechanism is that it may tend to cause the seat belt retractor to unnecessarily lock up to prevent belt protraction upon every application of the brake pedal. This may place unnecessary wear and tear on the retractor's components. Furthermore, during normal vehicle operation, it is desirable to move the upper torso for looking out the rear and rear quarter sides of the vehicle and for convenience, such as to reach about the vehicle.
It is also known that some activation mechanisms are activated by a variety of electric signals. An example of an electrical activated seat belt retractor is disclosed in U.S. Pat. No. 4,655,312. In this example, a seat belt retractor is actuated by an electric motor in response to a crash sensor. The disclosed crash sensor is an inertia activated switch or a simple radar system and causes the electric motor to be energized to remove most of the belt slack prior to a crash. A disadvantage is that this particular retractor relies entirely on an inertial mechanism to actually lock up the retractor against protraction of the seat belt during the crash. The electric motor only removes the belt slack prior to the inertial mechanism being activated by certain inertial forces to lock up the retractor against protraction of the belt.
It is apparent from the foregoing that there is a need for a seat belt retractor having an activation mechanism which may actuate the seat belt retractor either independently or in addition to the inertial mechanism to prevent seat belt protraction. It is also desired that the activation mechanism reduce unnecessary wear and tear on itself and the retractor.
An overall object is to provide an activation mechanism which is effective, efficient, durable and cost effective to manufacture, install and operate.
The present invention offers a solution to the aforedescribed problems by providing an activation mechanism which is readily applied to a retractor to actuate the retractor to prevent belt protraction in situations in which other activation mechanisms may not respond.